In an HSDPA communication mode whose standardization work is in progress based on 3GPP (3rd Generation Partnership Project), SHO (Soft Handover) is impossible and when a base station to which data is transmitted is changed due to shift of a terminal, HSDPA communication with a base station from which shift is made should be once cut off to make another connection with a base station to which the shift is made.
Accordingly, communication interruption time occurs at the time of switching a base station to hinder realization of real time service such as VoIP (Voice over IP) or the like on HSDPA. Under these circumstances, put on the table is HSDPA mobility enhancement as a mode for improving handover operation of HSDPA. Among them, consideration is given, as one mode of switching a communication destination base station, to a mode of receiving an HS-SCCH (High Speed Shared Control Channel) from both a base station from which shift is made and a base station to which the shift is made for a fixed time period and upon reception of HS-SCCH from the base station to which the shift is made, determining that an HSDPA serving cell is switched to thereafter execute HSDPA communication with the base station to which the shift is made.
One of handover methods as related art of HSDPA is recited, for example, in Literature 1. The handover method recited in Literature 1 includes an FCS requesting step of, when a mobile station in communication with a base station by a first cell detects a second cell of the same base station whose reception state is better than that of the first cell, transmitting an FCS request including second cell information, an FCS confirmation step of transmitting an FCS confirmation including FCS allowance information by using FCS-SCCH by a base station which has received an FCS request, a data transmission step of executing HARQ operation handover processing between the first cell and the second cell to transmit data yet to be transmitted by the second cell, and a data reception step of receiving data with a cell switched to the second cell by the mobile station which has received an FCS confirmation.
With this arrangement, a control procedure of FCS operation related to HSDPA and a signal transmission means are defined to realize improvement in efficiency and speed-up of handover.    Literature 1: Japanese Patent Laying-Open No. 2004-72513.
Among possible methods of avoiding a temporary cut-off of communication during handover processing is a method of, at the time of handover of HSDPA communication, receiving HS-SCCH from both a base station from which handover is made and a base station to which the handover is made for a fixed time period and when the HS-SCCH from the base station to which the handover is made includes self-directed data, determining that a base station is switched to thereafter receive HS-SCCH only from the base station to which the handover is made.
It is, however, necessary, at the time of confirming inclusion of self-directed data in HS-SCCH from the base station to which the handover is made as a base station switching determination criteria, to make determination based only on part 1 information of the HS-SCCH because HS-PDSCH (High Speed Physical Downlink Shared Channel) is transmitted before part 2 information of the HS-SCCH is all transmitted. The part 1 information, however, has no CRC (Cyclic Redundancy Check Code) added, so that error detection can not be checked to have a possibility of erroneous execution of base station switching.
In view of the above-described conditions, an object of the present invention is to provide a mobile communication method enabling a possibility of erroneous base station switching due to erroneous detection of a signal to be reduced to improve reliability of a mobile communication system. Another object of the present invention is to provide a mobile communication system enabling a possibility of erroneous base station switching due to erroneous detection of a signal to be reduced to improve reliability of the mobile communication system, and a mobile terminal thereof.